Digital Comm Lab Manual

LAB MANUAL
DIGITAL COMMUNICATION LAB

[KEC-651]
DEPARTMENT OF ELECTRONICS & COMMUNICATION
ENGINEERING
SHRI RAMSWAROOP MEMORIAL GROUP OF

PROFESSIONAL COLLEGES
AFFLIATED TO
DR. A. P. J. ABDUL KALAM TECHNICAL

UNIVERSITY
LUCKNOW, UP
SHRI RAMSWAROOP MEMORIAL GROUP OF PROFESSIONAL COLLEGES
B. TECH. (EC) VI SEM. (2020-21)
Digital Communication Lab (KEC-651)
INDEX
S No Name of Experiment CO Page(from…to...)
1 To study generation of Unipolar RZ & NRZ Line Coding. CO2 1–2
2 To study generation of Polar RZ & NRZ Line Coding. CO2 2–4
3 To study generation of Bipolar RZ & NRZ Line Coding. CO2 4–6
4 Implementation and analysis of BASK modulation and demodulation CO3 6–8
5 Implementation and analysis of BFSK modulation and demodulation CO3 8 – 11
6 Implementation and analysis of BPSK modulation and demodulation. CO3 11 – 14
7 Implementation and analysis of QPSK modulation and demodulation CO4 15 – 17
8 To study generation and detection of DPSK using MATLAB. CO4 18 – 20
9 Implementation and analysis of Delta modulation and demodulation. CO4 21 – 23
10 To study encoding and decoding of Linear Block Codes CO5 24 – 27
Course Outcomes (CO)

At the end of this course, the student will be able to:
CO1 : To formulate basic concepts of pulse shaping in digital communication.
CO2 : To identify different line coding techniques and demonstrate the concepts.
CO3 : To design equipment related to digital modulation and demodulation schemes.
CO4 : To analyze the performance of various digital communication systems and evaluate the key
parameters.
CO5 : To conceptualize error detection & correction using different coding schemes in digital
communication.
EXPERIMENT NO:-1
OBJECT: -To study generation of Unipolar RZ & NRZ Line Coding.
APPARATUS REQUIRED:
S.No. Instrument Required Specification Quantity
01 Training kit ST-2106 Scientech 1
02 CRO 20 MHz Scientech 1
03 Connecting Probes
THEORY: -
UNIPOLAR LINE CODING: -
Line coding is the process of converting digital data to digital signals.In Unipolar line coding all
the signal levels are either above or below the axis. It has only one voltage level other than zero.
The symbols 0&1 in digital system can represented in various formats with different levels and
wave forms. The selection of particular format for common pulse depends on the systems band
width, system’s ability to pass DC level information, error checking facility, case of clock
regeneration & synchronization at receiver, complexity & cost etc.
NON RETURN TO ZERO (LEVEL) NRZ: -

It is the simplest form of data representation. The NRZ waveform simply goes low for one bit
time to represent a data 0& high for one bit time to represent a data 1. It is unipolar line coding
scheme in which positive voltage defines bit 1 and the zero voltage defines bit 0. Signal does not
return to zero at the middle of the bit thus it is called NRZ.
RETURN TO ZERO (LEVEL) RZ: -

Return-to-zero (RZ or RTZ) describes a line code used in telecommunications signals in which
the signal drops (returns) to zero between each pulse. That "zero" condition is typically halfway
between the significant condition representing a 1 bit and the other significant condition
representing a 0 bit. RZ uses pulses at the start of the clock cycle to indicate a 1 value.
Fig.(1.1)
PROCEDURE:-
ECE Department, Prepared By Checked By

SRMGPC, Lko Page 1 of 27
Faculty In-charge Head of Department

1. Connect the ground, clock, data nodes of 8 bit variable data generator (ST2111) to clock, data
input & ground nodes of data formatting circuit.
2. Connect the CRO on the output node of unipolar NRZ available at data formatting circuit &
trace out the waveform.
3. Connect the CRO on the output node of unipolar RZ available at data formatting circuit &
trace out the waveform.
RESULT:-
Waveform of the unipolar NRZ& RZ format has been observed on CRO & traced out.
PRECAUTIONS:-
1. Don’t make loose connection.
2. Check the connection before switch ON the power supply.
3. Check the all-switch fault carefully.
RELATED QUESTIONS: -
Q.1 What is meant by Line coding?
Q.2 What is unipolar line coding?
Q.3 What do you mean by RZ and NRZ linecoding?
Q.4 Convert 1010 (binary data) in to digital waveform using unipolar RZ& NRZ line coding.
Q.5 What are advantages and disadvantages of unipolar line coding?


EXPERIMENT NO:-2
OBJECT:-To study generation of Polar RZ & NRZ Line Coding.
APPARATUS REQUIRED:
THEORY: -
POLAR LINE CODING: -
Line coding is the process of converting digital data to digital signals.In Polar line coding the
voltages are on the both sides of the axis.which means it will have both positive and negative
values for voltages or amplitude, it is quite like NRZ scheme but, here we have NRZ-L (i.e.,
NRZ-Level) and NRZ-I (i.e., NRZInvert).It has two voltage level other than zero. The symbols
0&1 in digital system can represented in various formats with different levels and wave forms.
The selection of particular format for common pulse depends on the systems band width, system’s
ability to pass DC level information, error checking facility, case of clock regeneration &
synchronization at receiver, complexity & cost etc.
NRZ-L AND NRZ-I –

These are somewhat similar to unipolar NRZ scheme but here we use two levels of amplitude
(voltages). For NRZ-L(NRZ-Level), the level of the voltage determines the value of the bit,
typically binary 1 maps to logic-level high, and binary 0 maps to logic-level low, and for NRZ-
I(NRZ-Invert), two-level signal has a transition at a boundary if the next bit that we are going to
transmit is a logical 1, and does not have a transition if the next bit that we are going to transmit is
a logical 0.
RETURN TO ZERO RZ: -

One solution to NRZ problem is the RZ scheme, which uses three values positive,negative,and
zero. In this scheme signal goes to 0 in the middle of each bit.The logic we are using here to
represent data is that for bit 1 half of the signal is represented by +V and half by zero voltage and
for bit 0 half of the signal is represented by -V and half by zero voltage.


Fig.2.1
PROCEDURE: -
1. Connect the ground, clock, data nodes of 8-bit variable data generator (ST2111) to clock, data
2. Connect the CRO on the output node of Unipolar NRZ-L, NRZ-I &RZ available at data
formatting circuit & trace out the waveform.
RESULT: -
Waveform of the Unipolar NRZ-L, NRZ-I &RZ format have been observed on CRO & traced
out.
PRECAUTIONS: -
RELATED QUESTIONS:-
Q.2 What is polar line coding?
Q.4 Convert 1010 (binary data) in to digital waveform using polar RZ& NRZ line coding.
Q.5 What are advantages and disadvantages of polar line coding?


EXPERIMENT NO:-3
OBJECT:-To study generation of Bipolar RZ & NRZ Line Coding.
APPARATUS REQUIRED:
THEORY: -
BIPOLAR LINE CODING: -
In this scheme there are three voltage levels positive, negative, and zero. The voltage level for one
data element is at zero, while the voltage level for the other element alternates between positive
and negative.Bipolar encoding, binary zero ('0') is represented by 0 voltage whereas binary one
('1) is represented by alternating positive and negative voltages. The Bipolar coding technique
uses different types of pulses based on which it is known as NRZ (Non-Return to Zero) or RZ
(Return to Zero).
NOT RETURN TO ZERO (NRZ): -

Uses three levels of signal level (+A, 0, -A)and has “Alternate Mark Inversion” (AMI).Bipolar
NRZ coding uses zero voltage to represent binary zero and +ve pulse and -ve pulse to represent
alternating binary ones during entire bit period. Hence pulse duration and symbol bit duration are
equal in NRZ type.
RETURN TO ZERO (RZ): -
Uses three levels of signal level (+A, 0, -A) has “Alternate Mark Inversion” (AMI). there is a
half-width +ve output pulse if the input isa ‘1’; or a half-width -ve output pulse if the input is a
‘0’. There is a return-to-zerofor the second half of each bit period.
Fig.3.1


PROCEDURE: -
1. Connect the ground, clock, data nodes of 8-bit variable data generator (ST2111) to clock, data
2. Connect the CRO on the output node of Bipolar NRZ &RZ available at data formatting circuit
& trace out the waveform.
RESULT: -
Waveform of the Bipolar NRZ &RZ format have been observed on CRO & traced out.
PRECAUTIONS: -
Q.2 What is bipolar line coding?
Q.4 Convert 1010 (binary data) in to digital waveform using unipolar RZ& NRZ line coding.
Q.5 What are advantages and disadvantages of polar line coding?


EXPERIMENT NO:-4
OBJECT: - Implementation and analysis of Binary Amplitude shift keying BASK modulation
and demodulation
APPARATUS REQUIRED: -
S. No. Apparatus name Specification Quantity
01 Transmitter kit ST-2106 Scientech 1
02 Receiver kit ST-2107 Scientech 1
03 8bit variable data generator ST-2111 Scientech 1
04 CRO 20MHz Scientech 1
THEORY: -
To transmit the digital data from one place to another, we have to choose the transmission
medium. It is not possible to send the digital data directly over the antenna because the antenna of
practical size works on very high frequencies much higher than our data transmission rate. To be
able to transmit the data over antenna, we have to MODULATE the carrier signal phase
frequencies or amplitude etc. which is varied in accordance with the digital data. At the receiver
we separate the signal from digital information by the process of “DEMODULATION”.
Modulation also allows different data streams to be transmitted our same channel.
This process is called as MULTPLEXING & result in a considerable saving of available
bandwidth. Some of the basic digital modulation techniques are ASK PSK & FSK.
BASK (BINARY AMPLITUDE SHIFT KEYING): -The simplest method of

modulating a carrier with a data stream is to change the amplitude of the carrier wave every time
the data changes. This modulation technique is known as “AMPLITUDE SHIFT KEYING”. The
simplest way of achieving amplitude shift keying is by switching on the carrier whenever the data
bit is 1 & switching off whenever the data bit is ‘0’ This technique is known as ON-OFF
KEYING. Thus
DATA = 1 CARRIER TRANSMITTED.
DATA = 0 CARRIER SUPPRESSED.
The BASK wave from is generated by balanced modulator circuit which is also known as a linear
multiplier. In order to generate ASK wave from we apply the digital data stream and modulation
input as a input to the linear multiplier. The method of demodulate the ASK wave from is to
rectify it pass it through the filter & square up the resulting wave from, the output is the original
data stream. Amplitude shift keying is less efficient because the noise inherent in the transmission
channel can deteriorate the signal so much that the amplitude changes in the modulated carrier
wave due to noise addition. This may lead to the incorrect decoding at the receiver. Hence THIS
TECHNIQUE IS NOT WIDELY USED IN PRACTICAL application & it ishowever used in
diverse areas and old emergency radio transmissions and fiber-optic communication.


Fig. 4.1
PROCEDURE:-
1. Connect the ground, clock, data nodes of 8 bit variable data generator (ST-2111) to clock,
data input & ground nodes of data formatting circuit.
2. Connect the output node of NRZ (L) available at node 5 to modulation I/P node of carrier
modulation circuit available at node 27.
3. Connect the node16 available at carrier generator circuit to node 26 available at carrier
generator circuit to node 26 available at carrier modulation circuit.
4. Do proper adjustments via carrier offset, gain and modulation offset nodes.
5. Connect the output node of carrier modulation circuit available at node 28 to CRO & trace
out the ASK waveform.
6. For Demodulation, connect the output of carrier modulation circuit available at node 28 to
the ASK demodulator available at node 21.
7. Connect the output node 22 of ASK demodulator to the input of LPF available at node 27.
8. Connect the CRO at LPF output available at node 28 &trace out the demodulated ASK wave
form.
RESULT:-
The study modulation &demodulation is completed.
PRECAUTIONS: -
1. Analyze the kit carefully.
2. Observe the wave form carefully.


3. Do all the connection at right position.
Q.1 What is modulation and demodulation?
Q.2 What is digital modulation and state various techniques?
Q.3 What do you mean by BPSK?
Q.4 What is multiplexing?
Q.5 Explain the need of modulation and demodulation.


EXPERIMENT NO:-5
OBJECT:- Implementation and analysis of Binary Frequency shift keying (BFSK) modulation
and demodulation.
APPARATUS REQUIRED: -
S.No. Apparatus name Specification Quantity
03 8 bit variable data generator ST-2111 Scientech 1
THEORY: -
In frequency shift keying the carrier frequency is shifted in steps i.e. from one frequency to one
particular value of data & another corresponding to another value of digital data. The higher
frequency is used to represented a data ‘1”& lower frequency a data ‘0’ thus,
DATA = 1: Higher frequency
DATA = 0: Low frequency
On a closer look at the BFSK wave, it can be represented as the sum of BASK wave forms.
BFSK MODULATION:-
Let us now apply the binary data stream to 1st BASK modulator using the high frequency carrier.
Let us now invert the original data stream.
Original 0110001011
Inverted 1001110100
Now apply the inverted data stream to the 2ndBASK modulator using a lower frequency carrier.
The result is the original data ‘0’ filled with lower frequency carrier& 1 is filled with higher
frequency carrier.
Finally, we will sum the two ASK waveform, to get the BFSK wave.
FSK DEMODULATION:-
The demodulation of FSK is done be using a phase locked loop which tries to ‘lock’ to the input
frequency. It is achieved by generating corresponding output voltage to be fed to the voltage-
controlled oscillator. If any frequency deviation at its input is encountered, the PLL follows the
frequency changes and generates proportional output voltage. The output of PLL contains carrier
components. Therefore, the signal is passed through the LPF to remove them. The resulting wave
is to be rounded off to be used for digital data processing. Also, the amplitude level may be very
low due to channel attenuation. Since the amplitude change in FSK wave form does not matter.
Thus it is a modulation technique which is very reliable even in noisy and fading channels. But


there is always a price to be paid to gain that advantage. Theprice in this case is widening of the
required bandwidth. The band width increase depends upon the two-carrier frequency used and
the digital data rate. The bandwidth required is at least double than inthe case of BASK
modulation.This means that lesser number of communication channels for a given band of
frequencies.
Fig 5.1BFSK modulation
Fig 5.2BFSK generator
PROCEDURE:-
1. Connect the ground, clock, data nodes of 8 bit variable data generator (ST-2111) to clock,
data input & ground nodes of data formatting circuit.
2. Connect the output node of NRZ (L) available at node 5 to modulation I/P node of carrier
modulation circuit available at node 27.
3. Connect the node16 available at carrier generator circuit to node 26 available at carrier
modulation circuit.
4. Do proper adjustments via carrier offset, gain and modulation offset nodes.
5. Connect the 960 KHz carrier frequency available at node 17 to node 29.


6. Connect the node 27 to input data inverter available at node 32.

7. Connect the output node of data inverter available at node 33to the modulation input available
at node 30.
8. Connect the output node 28 & 31 to the input A & B of summing amplifier available at node
34 & 35 respectively.
9. Connect the output summing amplifier available at node 36 to CRO &trace out the BFSK
waveform.
10. For Demodulation, connect the output of summing amplifier available at node 36 to the input
of FSK demodulator available at node 16.
11. Connect the output of BFSK demodulator available at node 17 to the input of LPF available
at node 23.
12. Connect the CRO to the output of LPF available at node 24 &trace out the BFSK
demodulated wave form.
RESULT:-
The study of BFSK modulation and demodulation is completed.
PRECAUTION:-
1. Connect the circuit carefully.
2. Observe the wave forms carefully.
RELATED QUESTIONS:-
Q.1 What is modulation and demodulation?

Q.2 What is digital modulation and state various techniques?
Q.3 What do you mean by BFSK?
Q.4 What is multiplexing?
Q.5 Explain the need of modulation and demodulation.


EXPERIMENT NO:-6
OBJECT:Implementation and analysis of BPSK modulation and demodulation.
APPARATUS REQUIRED:

03 Variable data generator ST-2111 Scientech 1
THEORY:
Binary Phase Shift Keying (BPSK) is digital transmission scheme where the binary data is
transmitted using out of phase signals. During logic ‘0’ a preset number of cycles of a sinusoidal
carrier signal is transmitted and during logic ‘1’ the same number of cycles of the carrier signal is
transmitted but with 1800 phase shift.0
MODULATOR:
A simple BPSK modulator circuit using an NPN-PNP transistor pair, and an Op-amp is shown in
figure. The transistors work as switches and the Op amp works as inverting/noninverting
amplifier. The carrier signal is fed to the collectors and the message signal is fed to the bases of
the two transistors simultaneously. The emitters of the transistors are grounded. When the
message signal is at logic ‘1’ (+5V), the NPN transistor is ON and works as a closed switch. The
PNP transistor is OFF and works as an open switch. The Op-amp now works as a non-inverting
amplifier with the carrier signal fed to its non-inverting input. The carrier signal reaches the
output without any phase shift. When the message signal is at logic ‘0’ (-5V), the NPN transistor
is OFF and the PNP transistor ON. The Op amp works as an inverting amplifier with the carrier
signal fed to its inverting pin. The carrier signal now reaches the output with 1800 phase shift.
Thus, the carrier signal switches its phase as the message signal switches between ‘0’ and ‘1’. The
resulting output is BPSK modulated.
DEMODULATOR:
The BPSK demodulator circuit shown in figure consists of an Op-Amp difference amplifier, a
rectifier, an envelope detector and a comparator. The difference amplifier which is fed with the
unmodulated carrier signal at the non-inverting input and the BPSK modulated signal at the
inverting input passes only the phase shifted signal to the output. The in phase signals get
subtracted completely. The envelope detector removes the carrier content and recovers the data
information. The comparator inverts and level limits the signal to regain the correct logic level.


PROCEDURE:
1. Test all the components and probes.

2. Set up the circuits on the bread board as shown in figure.
3. Feed 2Vpp, 1KHz sine wave as carrier input and 10Vpp, 200Hz square wave signal as the
message input.
4. Observe the BPSK output on CRO and plot the waveforms.
5. Feed this BPSK modulated signal to the inverting input of the demodulator. Also feed the
unmodulated carrier signal (2Vpp, 1KHz) to the non-inverting input.
6. Observe waveforms on CRO. Adjust the potentiometer to obtain the correct output (if needed).
7. Plot the waveforms.
CIRCUIT DIAGRAM:
WAVEFORM:


RESULT:-
BPSK modulator and demodulator circuits were set up and the waveforms were plotted.
PRECAUTION:-
1. Connect the circuit carefully.

2. Observe the wave forms carefully.
RELATED QUESTIONS:-
Q.1 What is the phase difference between the two transmitted signals through BPSK
scheme?
Q.2 Express the BPSK signal mathematically.
Q.3 State the Euclidean distance for BPSK.
Q.4 What is advantage and disadvantage of BPSK receiver?
Q.5 Which type of receiver is used for BPSK detection?


EXPERIMENT NO:-7
OBJECT: Implementation and analysis of QPSK modulation and demodulation
APPARATUS REQUIRED:

03 8 bit variable data generator ST-2111 Scientech 1
THEORY:
QPSK is also known as quaternary PSK, quadri phase PSK, 4-PSK, or 4-QAM. It is a phase
modulation technique that transmits two bits in four modulation states. Phase of the carrier takes
on one of four equally spaced values such as π/4, 3π/4, 5π/4and7π/4.
Si(t) = √2E/T cos {2 πƒct + (2i – 1) π/4} , 0≤ t ≤Tb ,
=0 elsewhere
Where i = 1,2,3,4, & E= Tx signal energy per symbol, T= symbol duration.
Each of the possible value of phase corresponds to a pair of bits called dibits. Thus, the gray
encoded set of digits: 10,00,01,11
Si (t) = √2E/T cos [(2i – 1)π/4] cos (2πfct) - √2E/T sin [(2i –1) π/4)] sin (2πfct) ,0≤ t ≤Tb
= 0 , elsewhere
There are two orthonormal basis functions.

c1 (t) = √2/T cos 2πƒct, 0≤ t ≤Tb
c2 (t) = √2/T sin 2πƒct, 0≤ t ≤Tb
There are four message points
Phase of QPSK Co-ordinates of message signals

Input debits signal
S1 S2
10 π/4 √E/2 -√E/2
00 3π/4 -√E/2 -√E/2
01 5π/4 -√E/2 +√E/2


11 7π/4 +√E/2 +√E/2
The I/p binary sequence b(t) is represented in polar from with symbols 1 & 0 represented as
+√E/2 and -√E/2. This binary wave is demultiplexed into two separate binary waves consisting of
odd & even numbered I/P bits denoted by b1 (t) & b2 (t). b1 (t) & b2 (t) are used to modulate a pair
of quadrature carrier. The result is two PSK waves. These two binary PSK waves are added to
produce the desired QPSK signal
Figure. 7.1: Block diagram of QPSK Transmitter
Figure 7.2: Block diagram of QPSK Receiver
QPSK receiver consists of a pair of correlators with common I/P & supplied with locally
generated signal c1 (t) & c2 (t). The correlator output, x1, & x2 are each compared with a
threshold of zero volt. If x1 > 0, decision is made in favour of symbol‘1’forupper channel and if


x1 > 0, decision is made in favour of symbol 0. Parallelly if x2 >0, decision is made in favour of
symbol 1 for lower channel & if x2 <0, decision is made in favour of symbol 0. These two
channels are combined in a multiplexer to get the original binary output.
PROCEDURE:
1. Test all the components and probes.
2. Set up the circuits on the kit.
3. Feed 2Vpp, 1KHz sine wave as carrier input and 10Vpp, 200Hz square wave signal as the
message input.
4. Observe the QPSK output on CRO and plot the waveforms.
5. Feed this QPSK modulated signal to the inverting input of the demodulator. Also feed the
unmodulated carrier signal (2Vpp, 1KHz) to the non-inverting input.
6. Observe waveforms on CRO. Adjust the potentiometer to obtain the correct output (if needed).
7. Plot the waveforms.
WAVEFORM:
The QPSK waveform for two-bits input is as follows, which shows the modulated result for
different instances of binary inputs.
RELATED QUESTIONS:-
Q.1 Write down the QPSK signal mathematically.

Q.2 What is the phase difference between the adjacent messages in QPSK ?
Q.3 What is the phase difference between the adjacent messages in QPSK ?
Q.4 Discuss the application of QPSK technique.
Q.5 What are the advantages of QPSK system ?


EXPERIMENT NO:-8
OBJECT: - To Simulate differential phase shift keying technique using MATLAB software
and also observe its performance.
APPARTUS USED: - PC
THEORY:-
DPSK involves 2 basic operations at the transmitter, differential encoding of the i/p binary wave
and phase shift keying, hence the name DPSK. In the differential encoding at the transmitter
input, starts with an arbitrary first bit serving as reference and thereafter the sequence is generated
using b(t) -1' previous value of differentially encoded digit d(t) i/p binary digit at time k Tb.
Assuming reference bit added to b(t) is a'1'. B(k) is thus generated and used to phase shift key a
carrier with phase angles 0 and 1800 .
BER -Bit Error Rate
In digital transmission, the number of bit errors is the number of received bits of a data stream
over a communication channel that has been altered due to noise, interference, distortion or bit
synchronization errors. The bit error rate or bit error ratio (BER) is the number of bit errors
divided by the total number of transferred bits during a studied time interval. BER is a unitless
performance measure, often expressed as a percentage. In a communication system, the receiver
side BER may be affected by transmission channel noise, interference, distortion, bit
synchronization problems, attenuation, wireless multipath fading, etc. The BER may be analyzed
using stochastic computer simulations. If a simple transmission channel model and data source
model is assumed, the BER may also be calculated using Binary symmetric channel (used in
analysis of decoding error probability in case of non bursty bit errors on the transmission channel)
and Additive white gaussian noise (AWGN) channel without fading.
Algorithm * To send ‘0’ and ‘1’following

Consideration is adopted.
Initialization commands
1. Generate the input data randomly ‘1’- no phase change
2. Implement differential encoding ‘0’- phase change of 1800
3. Do BPSK modulation or
4. Add AWGN noise ‘1’ – phase change of 1800
5. Calculate the no of bits in error
6. Plot the BER graph ‘ 0’ – no phase change
# Let d (t) = 1 1 0 1 0 1 1 1
Phase = 0 0 1800 0 1800 0 0 0 -- ‘1’ no change


TRANSMITTER CIRCUIT: -
d (t) = 1 1 0 1 1 0 1 0 1 0 1
b (t) = 1 1 1 0 0 0 1 1 0 0 1 1
(Let)
RECEIVER CIRCUIT:-
DPSK Demodulator


PROGRAM :-
N = 10^4 % number of bits or symbols
rand('state',100); % initializing the rand() function
randn('state',200);% initializing the randn() function
ip = rand(1,N)>0.5;% generating 0,1 with equal probability
ipD = mod(filter(1,[1 -1],ip),2); % %differential encoding y[n]=y[n-1]+x[n]
s = 2*ipD-1; % BPSK modulation 0 -> -1; 1 -> 0
n = 1/sqrt(2)*[randn(1,N) + j*randn(1,N)]; % white gaussian noise, 0dB variance
Eb_N0_dB = [-3:10]; % multiple Eb/N0 values
for ii = 1:length(Eb_N0_dB)
y = s + 10^(-Eb_N0_dB(ii)/20)*n; % additive white gaussian noise
ipDHat_coh = real(y) > 0; % coherent demodulation
ipHat_coh = mod(filter([1 -1],1,ipDHat_coh),2); %differential decoding
nErr_dbpsk_coh(ii) = size(find([ip - ipHat_coh]),2); % counting the number of errors
end
simBer_dbpsk_coh = nErr_dbpsk_coh/N;
theoryBer_dbpsk_coh = erfc(sqrt(10.^(Eb_N0_dB/10))).*(1 - .5*erfc(sqrt(10.^(Eb_N0_dB/10))));
close all
figure
semilogy(Eb_N0_dB,theoryBer_dbpsk_coh,'b.-');
hold on
semilogy(Eb_N0_dB,simBer_dbpsk_coh,'mx-');
axis([-2 10 10^-6 0.5])
grid on
legend('theory', 'simulation');
xlabel('Eb/No, dB')
ylabel('Bit Error Rate')
title('Bit error probability curve for coherent demodulation of DBPSK')
RESULT:-
1. Simulation of DPSK is done.
2. Performance is observed by measuring the BER characteristics. Characteristics are similar to
theoretical result.
RELATED QUESTIONS:-
Q.1 What is the DPSK?

Q.2 Write down the advantages of DPSK.
Q.3 Discuss the disadvantages of DPSK.
Q.4 Which method is commonly used in modulation and demodulation of DPSK?
Q.5 Write down the application of DPSK.


EXPERIMENT NO:-9
OBJECT:Implementation and analysis of Delta modulation and demodulation.
APPARATUS USED:
SNO APPARATUS NAME SPECIFICATION QUANTITY
03 Connecting Probes 2
THEORY:
Delta modulation is a system of digital modulation scheme in which the difference between the
sample value at sampling time K and sampling value at previous sampling time (K-1) is encoded
into just a single bit. One way in which delta modulator and demodulator is assembles is as shown


es is as shown


in figure given below
RELATED QUESTIONS:-
Q.1 In predictive coding, differentiate between DM and ADM.

Q.2 In predictive coding, differentiate between DPCM and ADPCM.
Q.3 What are slope overload distortion and granular noise distortion in DM coding?
Q.4 Explain how ADM coding solves the above errors.
Q.5 What is the difference between DM and DPCM?


EXPERIMENT NO:-10
OBJECT:To study encoding and decoding of Linear Block Codes
APPARATUS REQUIRED:
SNO APPARATUS NAME SPECIFICATION QUANTITY

01 Training kit ST-2121A & 2121B 1
Scientech
02 Banana Cable 2 mm 1
03 Regulated Power Supply
THEORY:
Error Detection and Correction: Error detection is the ability to detect the presence of errors
caused by noise or other impairments during transmission from the transmitter to the receiver.
Error correction is the additional ability to reconstruct the original, error-free data. There are two
basic ways to design the channel code and protocol for an error correcting system.
LINEAR BLOCK CODES:

Linear block codes are conceptually simple codes that are basically an extension of single-bit parity
check codes for error detection. A single-bit parity check code is one of the most common forms
of detecting transmission errors. This code uses one extra bit in a block of n data bits to indicate
whether the number of 1s in a block is odd or even. Thus, if a single error occurs, either the parity
bit is corrupted or the number of detected 1s in the information bit sequence will be different from
the number used to compute the parity bit: in either case the parity bit will not correspond to the
number of detected 1s in the information bit sequence, so the single error is detected. Linear block
codes extend this notion by using a larger number of parity bits to either detect more than one
error or correct for one or more errors. Unfortunately, linear block codes, along with convolutional
codes, trade their error detection or correction capability for either andwidth expansion or a lower
data rate, as will be discussed in more detail below. We will strict our attention to binary codes,
where both the original information and the corresponding code consist of bits taking a value of
either 0 or 1.


ENCODING


DECODING:-
The decoding process is done in the following steps:
RESULTS:
The understanding of modulation and demodulation schemes for linear block code developed.
RELATED QUESTIONS:-
Q.1 What is the definition of a linear block code?

Q.2 If we want to be able to detect two-bit errors, what should be the minimum Hamming
distance?
Q.3 In a codeword, we add two redundant bits to each 8-bit data word. Find the number of
(a) Valid codeword(b) Invalid codeword
Q.4 What is the minimum distance in linear block codes?
Q.5 What is the Hamming distance for each of the following codewords?
(a) (10000, 00000) (b) (10101, 10000) (c) (00000, 11111) (d) (00000, 00000)


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LAB MANUAL

DIGITAL COMMUNICATION LAB

SHRI RAMSWAROOP MEMORIAL GROUP OF

DR. A. P. J. ABDUL KALAM TECHNICAL

1 To study generation of Unipolar RZ & NRZ Line Coding. CO2 1–2

2 To study generation of Polar RZ & NRZ Line Coding. CO2 2–4

3 To study generation of Bipolar RZ & NRZ Line Coding. CO2 4–6

4 Implementation and analysis of BASK modulation and demodulation CO3 6–8

5 Implementation and analysis of BFSK modulation and demodulation CO3 8 – 11

6 Implementation and analysis of BPSK modulation and demodulation. CO3 11 – 14

7 Implementation and analysis of QPSK modulation and demodulation CO4 15 – 17

8 To study generation and detection of DPSK using MATLAB. CO4 18 – 20

9 Implementation and analysis of Delta modulation and demodulation. CO4 21 – 23

10 To study encoding and decoding of Linear Block Codes CO5 24 – 27

Course Outcomes (CO)

NON RETURN TO ZERO (LEVEL) NRZ: -

RETURN TO ZERO (LEVEL) RZ: -

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NRZ-L AND NRZ-I –

RETURN TO ZERO RZ: -

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NOT RETURN TO ZERO (NRZ): -

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BASK (BINARY AMPLITUDE SHIFT KEYING): -The simplest method of

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3. Do all the connection at right position.

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Fig 5.1BFSK modulation

Fig 5.2BFSK generator

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6. Connect the node 27 to input data inverter available at node 32.

Q.1 What is modulation and demodulation?

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S.No. Apparatus name Specification Quantity

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1. Test all the components and probes.

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1. Connect the circuit carefully.

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